Up-Date of a Thermodynamic Database of the ZrO2-Gd2O3-Y2O3-Al2O3 System for TBC Applications

The thermodynamic database of the ZrO2-Gd2O3-Y2O3-Al2O3 system is up-dated taking into account new data on lattice stabilities of ZrO2, Gd2O3 and Y2O3 and heat capacity measurements for the monoclinic phase Gd4Al2O9 and phase with garnet structure Gd3Al5O12. New data for the heat capacities of Gd2Zr2O7 (pyrochlore) and GdAlO3 (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr1-x Gd (x) )O2-x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd4Al2O9 phase from a peritectic one to a congruent one in the Gd2O3-Al2O3 system. Correspondently, in the ternary system ZrO2-Gd2O3-Al2O3, the melting character of the three-phase assemblage Gd2O3 (B), Gd4Al2O9 and GdAlO3 changed from eutectic to transition type U. The T (0)-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO2-Gd2O3-Y2O3 system.